This invention relates generally to weighing scales and more particularly to beam scales of the type used by doctors to weigh their patients.
Typically, the beam scale involves a platform with some type of force collecting lever arrangement and an adjacent column supporting a balance beam which is interconnected by levers and links to the force collecting means associated with the platform. The force applied to the platform is transmitted to one end of the pivoted beam and adjustable weights are supported on the beam on the other side of the pivot to permit the user to balance the force applied to the platform by adjusting the distance of the weights from the pivot point. Such a scale has provided accurate and reliable weight information but requires some skill and experience to operate it properly. In addition, the adjustment of the weights and the balancing of the beam accurately is time consuming.
With the availability of inexpensive microprocessors, the weighing scale industry has been moving in recent years toward the use of electrical and electronic measuring and indicating means for weighing scales. These scales involve the use of either electronic means for measuring and displaying the displacement of the conventional spring biased platforms or the use of strain gages to produce an electrical signal proportional to the applied load and circuit means for converting this signal into a display of the weight. Many different approaches have been employed in the location and positioning of the strain gages in order to obtain an accurate and consistent response to the load applied to the scale. Various arrangements of mechanical levers have been used to collect the force and apply such force to one or more flexible beams to which the strain gages may be affixed. The deflection of such beams are sensed by the strain gages, giving an indication of the load applied to the scale. Examples of several of such prior art strain gage scales are shown in the patents to Provi et al U.S. Pat. No. 4,050,532, Provi U.S. Pat. No. 4,457,385, Belcher U.S. Pat. No. 4,223,752, Jushmuck U.S. Pat. No. 4,241,801 and Oejelid U.S. Pat. No. 3,894,594.
It has also been known in the prior art to use strain gage measuring means in connection with beam scales. Examples of such scales are shown in the patents to Nyhold U.S. Pat. No. 4,036,318 and Fletcher et al U.S. Pat. No. 3,812,924 and Storace U.S. Pat. No. 4,113,040. The Nyholm patent discloses a lever equipped with strain gages to measure the deflection of a balance beam and thereby produce a weight indication. In the Storace patent, the strain gage is used to sense unbalance of the beam and to rebalance it rather than to produce a signal the magnitude of which indicates the weight measurement. The Fletcher patent employs a balance beam with a flexible support monitored by a strain gage to measure changes in the weight of a specimen.
It has also been known in the prior art to combine beam scales with mechanisms which permit use of the adjustable weights of the beam scale along with a separate readout mechanism which will avoid the time consuming chore of making the vernier weight adjustments to arrive at the total weight. One such patent in Stahmer U.S. Pat. No. 3,227,233. In the Stahmer patent, the total weight in the scale is obtained by adding the weight indicated by the slidable weight position to the reading provided by a dial indicator on the scale. It is also known in the prior art to provide a beam scale with means for automatically applying and removing weights of the beam to balance the applied load. This type of mechanism is shown in the patent to DeMasters et al U.S. Pat. No. 4,106,580. The DeMasters et al patent uses load cells or differential transformers to automatically rebalance the beam of the scale disclosed therein.
None of the above-cited prior art patents discloses a practical balance beam scale utilizing a strain gage sensing mechanism.